His little sister is affecting our relationship i need advice?

Okay i posted something last month about this my boyfriends little sister likes to play around by saying oh stinky butt stuff like that but when you tell her something that she cant top off she gets all mad now my boyfriend is super overprotective of her he babys her and now she is spoiled and she's 7 she wants a lap top computer by the age of 10 so she gets mad when she doesnt get what she wants so... last night i went over his dogs had puppies and i told her im going to keep this one but i said it nicely and told her you cant afford to keep all four we dont have enough money so she got all upset. My issue is my boyfried told me to ignore her when she gets this and im not about to get sad and let this get to me so he got mad at me every time we argue or fight is because of her i dont know what to do anymore its frustrating WE DONT FIGHT ABOUT ANYTHING ELSE JUST WHEN IT COMES TO HER i do what he says but then when i ignore her he gets mad and tells me YOU DONT CARE i need advice..His little sister is affecting our relationship i need advice?
that's a hard one, I have 2 little twin sisters who are some what spoiled, when my girl comes to our house they are the same way, but I know they are just doing that because I'm their big brother and I have a another girl there who is not them and is getting my attention, there just being little sisters, don't take it to hart to much, humor her, don't ignore you might as well be mean to her, its the same thing, and don't try to make him choose , all that puppy jazz, the parents will remedy that situation, but its kind of funny you trying to compete with a little kid, good luck

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